The present invention relates in general to a method of and a device for cladding elongated objects, such as wires and the like, with a material of different composition, preferably powdered metals resulting in a metallurgically bonded cladding.
From the prior art various methods are known for casting a thick metal layer around a metal strand. In one of these methods, the metal strand is heated in a preliminary heating zone to a temperature exceeding that which is necessary for inner bonding of the cast coating with the strand material but which is longer than the melting temperature of the cast layer. The metal strand in this known method is exposed to the casting metal in a bath through which it passes at a speed adjusted in accordance with the exposed length so as to produce a progressively increasing layer of the cast metal on the strand surface (German Pat. No. 1,521,195). This known over-casting method has the disadvantage that due to the passage of the strand through the molten metal the crystalline structure of the strand metal is changed and also other undesired phenomena will take place.
In another prior-art method the wire is first guided through an alignment apparatus, then through a cleaning device; thereafter it is guided through a bottom part of a funnel in which powdered metal to be applied thereon is stored and finally it passes through a set of rollers rotating in feeding direction of the wire. In this manner, however, the wire can be sprinkled only with a very thin layer of the powdered metal and as described, for example, in U.S. Pat. No. 3,088,195, this method is especially applicable for powdered aluminum. The rollers for impressing the powder layer into the wire act upon the latter in perpendicular direction and cause the powdered metal to bond to the wire surface. Thereupon an after-treatment in a furnace and in an additional rolling device takes place, then a tempering in a tempering furnace and subsequently before winding of the cladded wire in a winding machine, the wire is subjected again to a rolling process in several sets of rollers, all of which act in perpendicular direction to the axis of the processed wire. The main disadvantage of this rather complicated cladding process is the perpendicular arrangement of cladding rollers by which the powdered metal is cladded almost exactly in axial direction of the strand. As a result, the finished product has axially extending zones of modified grain structures which considerably influence the strength of the wire and impart thereto metallurgically unfavorable properties which even after a complicated aftertreatment cannot be completely removed.